Method for producing liquid pig iron

ABSTRACT

Process and apparatus for producing liquid pig iron or primary steel products from iron-containing material in lump form in a fusion gasifier ( 1 ), in which, with lump coal and oxygen-containing gas being fed in, and with simultaneous formation of a reduction gas, the iron-containing material is fused, lump coal being fed to the fusion gasifier ( 1 ) from above and, together with the iron-containing material, forming a fixed bed ( 6 ) in the fusion gasifier ( 1 ) and thereby giving off its fraction of volatile hydrocarbons into the dome space ( 11 ) located above the fixed bed ( 6 ), and pulverized-fuel burners ( 15 ) being directed obliquely from above towards the surface of the fixed bed ( 6 ). The operation of the pulverized-fuel burners ( 15 ) is in this case controlled in such a way that the combustion of the carbon fraction of the carbon carriers in fine particle form takes place in a proportion of at least 40% to form CO 2 .

BACKGROUND OF THE INVENTION

The invention relates to a process and apparatus for producing liquidpig iron or primary steel products from iron-containing material in lumpform, such as partly and/or fully reduced iron sponge, in a fusiongasifier, in which, with lump coal and possibly other carbon-containingmaterial and oxygen-containing gas being fed in, and with simultaneousformation of a reduction gas, the iron-containing material is fused,possibly after prior full reduction, lump coal being fed to the fusiongasifier from above and, together with the iron-containing material,forming a fixed bed in the fusion gasifier, thereby giving off itsfraction of volatile hydrocarbons into the dome space located above thefixed bed, pulverized-fuel burners, which are operated with a carboncarrier in fine particle form and an oxygen-containing gas, passingthrough the shell of the fusion gasifier in a horizontal cross-sectionalplane of the dome space at approximately equal distances from oneanother and being directed obliquely from above towards the surface ofthe fixed bed.

In processes of the type described above, it is known to feed lump coaldirectly to the fusion gasifier as a source of energy. The coal is inthis case fed to the fusion gasifier from above and subjected to shockheating in the fusion gasifier because of the temperatures prevailingtherein. The heating of the coal in this pyrolysis step causes itscontent of volatile hydrocarbons to be driven out and given off as gasinto the dome space. Since it is necessary to convert the hydrocarbonsin the reduction gas that are released during the pyrolysis, until now adome temperature of approximately 1050° C. has been required to ensurethermal decomposition within a specific residence time in the fusiongasifier.

This thermal decomposition results in that, apart from hydrogen, carbonin the form of soot is formed as a reduction gas component according tothe equation:

resulting in an additional, very fine-grained dust burden.

Owing to the size of the dome space and low gas velocities, uneven gasdistribution and consequently inhomogeneous gas mixing occurs. Thisleads to inadequate heating of coal particles located in critical zones,consequently to incomplete degasification, with the result that the coaldust which is drawn off with the reduction gas from the fusion gasifiertends to agglomerate.

A further effect of the inadequate gas mixing in the dome space is thatthe residence time of the hydrocarbons in critical zones of the domespace is not adequate to ensure their complete thermal decomposition.This in turn has adverse effects on the reduction potential of thereduction gas drawn off from the fusion gasifier.

It is also known to feed additional energy to the fusion gasifierthrough pulverized-fuel burners directed obliquely from above towardsthe surface of the fixed bed. Such burners are operated with carboncarriers in fine particle form, usually carbon-containing, dust derivedfrom the process and an oxygen-containing gas, for example industrialoxygen or air. The operation of these pulverized-fuel burners usuallytakes place substoichiometrically, i.e. apart from introducingadditional energy into the fusion gasifying process, the purpose of thepulverized-fuel burners is to generate reduction gas components (CO andH₂).

SUMMARY OF THE INVENTION

The object of the present invention is thus to provide a process inwhich the reaction conditions in the dome space of the fusion gasifierare set in such a way that the formation of soot during thedecomposition of hydrocarbons driven out from the coal is largelyprevented. It is intended overall for the dust burden carried by thereduction gas from the fusion gasifier to be reduced and also for thetendency of the dust to agglomerate to be reduced.

This object is achieved according to the invention by the operation ofthe pulverized-fuel burners with a carbon carrier in fine particle form,with oxygen-containing gas being controlled in such a way that thecombustion of the carbon fraction of the carbon carrier in fine particleform takes place—in a way corresponding to the set stoichiometry—in aproportion of at least 40% to form CO₂, whereby the volatilehydrocarbons given off by the coal are converted in an oxidizing manner.

The CO₂, which flows from the burners to the place where thehydrocarbons are released, causes the latter to be converted no longerthermally (see above), but in an oxidizing manner, according to theequation:

C_(n)H_(m) +nCO₂→2nCO+m/2H₂  (II)

It is known from the prior art that this reaction proceeds adequatelyrapidly even at relatively low temperatures in the presence of acatalyst, for example Fe dust, which is in any event present insufficient quantity in the dome space of the fusion gasifier.

The process according to the invention makes it possible for the firsttime for the thermal decomposition of the hydrocarbons driven out of thecoal to form hydrogen and soot to be largely prevented and at the sametime for additional reduction gas components to be obtained.

According to a preferred embodiment of the process according to theinvention, the operation of the pulverized-fuel burners is controlled insuch a way that the combustion of the carbon fraction of the carboncarrier in fine particle form takes place in a proportion of at least70% to form CO₂.

Since the thermal decomposition and oxidizing conversion of thehydrocarbons are reactions competing with one another, it is ofadvantage if the oxidizing conversion is favored by offering moreor—with respect to the hydrocarbons—an excess of oxidants in the domespace.

According to a further embodiment of the process according to theinvention, the pulverized-fuel burners are aligned in such a way that agas-mixing turbulent flow is generated in the dome space by the burnerflames.

The generation of a gas-mixing turbulent flow has the effect on the onehand of ensuring a more even mixing through and consequent warmingthrough of all the gases and solid particles located in the dome space,and on the other hand, of also making the residence times of the gasesand solids in the dome space more uniform, so that consequently afuller, ideally complete, oxidizing conversion of the hydrocarbons ismade possible.

For generating this gas-mixing turbulent flow, it is of advantage if thepulverized-fuel burners are aligned along lines extending askew in thesame sense with respect to the vertical central axis of the fusiongasifier.

The pulverized-fuel burners are thus directed obliquely downwards,proceeding from the shell of the fusion gasifier, but are not aligned ina converging manner, that is not towards the vertical central axis ofthe fusion gasifier, but “point” to a certain extent past the centralaxis.

This embodiment has the advantage that the pulverized-fuel burnersgenerate a spiral-form turbulent flow, which is particularly suited foreven mixing of the components of the dome space and for making theirresidence time more uniform.

A further advantage is that the burner flames are not directed straightat the charging point of the coal, that is the central region of thesurface of the fixed bed, thereby preventing excessive thermal graindisintegration being caused by abrupt degasification.

Further subject-matter of the invention concerns an apparatus forproducing pig iron or primary steel material from iron-containingmaterial in lump form, such as partly and/or fully reduced iron sponge,with a fusion gasifier provided with a charging device for lump coal, areduction-gas discharge line with a solids separator for drawing offgenerated reduction gas, a gas line for oxygen-containing gas, a feedingdevice for the iron-containing material, a run-off for molten slag andmolten pig iron, as well as with pulverized-fuel burners, eachpulverized-fuel burner being provided with a dust line for carboncarriers in fine particle form and a supply line for oxygen-containinggas, a lower portion of the fusion gasifier being provided for receivingliquid pig iron or primary steel material and liquid slag, a centralportion for receiving a fixed bed of lump coal and iron-containingmaterial in lump form, as well as an upper portion as a dome space, thepulverized-fuel burners passing through the shell of the fusion gasifierin a portion at a specific height of the dome space and being arrangedessentially evenly spaced from one another and directed obliquely fromabove towards the surface of the fixed bed.

Such an apparatus is characterized according to the invention in thatthe charging device for lump coal is arranged in such a way that thefeeding direction of the lump coal is aligned essentially in line withthe vertical central axis of the fusion gasifier and in that thepulverized-fuel burners are aligned along lines extending askew in thesame sense with respect to the vertical central axis of the fusiongasifier, the pulverized-fuel burners with the dust line and the supplyline being designed for an at least 40% conversion of the carbonfraction of the carbon carrier in fine particle form into CO₂.

According to an advantageous feature of the apparatus according to theinvention, the lines along which pulverized-fuel burners are alignedhave in each case the same normal distance from the vertical centralaxis of the fusion gasifier.

To be understood here as the normal distance is the distance between twostraight lines measured along a third straight line which, with the twoother straight lines, that is the line along with a pulverized-fuelburner is aligned and the vertical central axis of the fusion gasifier,in each case encloses a right angle.

A turbulent flow which utilizes the geometry of the fusion gasifier orof the dome space particularly advantageously, in particular aspiral-form turbulent flow, can be achieved in this way.

According to a further feature of the apparatus according to theinvention, two to six, preferably four, pulverized-fuel burners whichare evenly spaced from one another and pass through the shell of thefusion gasifier are provided.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention is illustrated in the drawings FIG. 1 and FIG. 2.

FIG. 1 schematically shows a vertical section through a fusion gasifier.

FIG. 2 represents a horizontal section through the fusion gasifier.

DESCRIPTION OF PREFERRED EMBODIMENT

The fusion gasifier 1 is fed lump coal via a charging device 2, forexample a screw conveyor system. By means of a feeding device 3, thefusion gasifier 1 is also fed iron-containing material in lump form, forexample iron sponge. The fusion gasifier 1 is also fed, via gas lines 4,an oxygen-containing gas, in particular industrial oxygen, as obtainedfrom an air fractionation plant.

Lump coal and iron sponge form in a central portion 5 of the fusiongasifier 1 a fixed bed 6, in which the lump coal is gasified by means ofthe oxygen-containing gas to form a CO- and H₂-containing reduction gas,and the iron sponge is thereby possibly fully reduced and smelted toform liquid pig iron.

Molten slag 8 and molten pig iron 9, which are tapped via a run-off 10,collect in a lower portion 7 of the fusion gasifier 1.

The reduction gas formed during gasifying of the coal is drawn off outof the upper portion 12—formed by a dome space 11—of the fusion gasifier1 via a reduction-gas discharge line 13 and dedusted in a solidsseparator 14, for example a hot cyclone.

Above the fixed bed 6, pulverized-fuel burners 15 pass through the shellof the fusion gasifier 1 in such a way that, during operation of thepulverized-fuel burners 15, the burner flames 16 are directed obliquelyfrom above towards the surface of the fixed bed 6. Each of thepulverized-fuel burners 15 has a dust supply line 17 for carbon carriersin fine particle form, for example dust deposited in the solidsseparator 14, as well as a supply line 18 for oxygen-containing gas.

FIG. 2 represents a horizontal section through the fusion gasifier 1,for instance at the level of the pulverized-fuel burners 15.

The pulverized-fuel burners 15 are arranged in such a way that they aredirected obliquely from above towards the surface of the fixed bed(FIG. 1) and point past the center of the fusion gasifier 1, that isthey extend askew with respect to the vertical central axis of thefusion gasifier 1.

This arrangement of the pulverized-fuel burners 15 has the effect thatthe gases and solid particles rising up out of the fixed bed 6 andlocated in the dome space 11 are set into a rotating turbulent flow 20,achieving the overall effect of making the residence time of all the gasand solid components in the dome space 1 more uniform and consequentlyimproving the mixing through.

The charging device 2 for lump coal opens out into the fusion gasifier 1essentially in line with the vertical central axis 19. The individualpieces of coal are thus not exposed directly to the heat action of theburner flames 16, thereby avoiding pieces of coal exploding due toabrupt heating or degasification.

When the coal meets the fixed bed, the coal gives off its volatileconstituents (hydrocarbons, tar components) in a pyrolysis step. Theoperation of the pulverized-fuel burners is controlled in such a waythat the carbon fraction of the carbon carriers in fine particle formfed via dust lines 17 burns in a proportion of at least 40% to form CO₂.

The volatile constituents give off by the coal are either converteddirectly after release in an oxidizing manner according to equation(II), by the “CO₂ streams” directed at the place where they arereleased, or are mixed with one another, by the turbulent flowprevailing in the dome space 11, and consequently converted for the mostpart, the iron dust carried with the reduction and other gases out ofthe fixed bed 6 into the dome space 11 acting in a catalyzing manner.

The process according to the invention and the apparatus according tothe invention make possible a largely complete oxidizing conversion ofthe hydrocarbons given off with the volatile constituents from coal,whereby the fraction of the volatile constituents thermally decomposedaccording to equation (I) to form soot is greatly reduced and the dustburden carried with the reduction gas out of the fusion gasifier 1causes no or significantly less caking in downstream apparatuses.

The invention is not restricted to the exemplary embodiment representedin the FIG. 1 and FIG. 2, but also covers all the means known to aperson skilled in the art that can be used for implementing theinvention.

What is claimed is:
 1. Process for producing liquid pig iron or primarysteel products from iron-containing material in lump form in a fusiongasifier enclosed by a shell, in which, with lump coal and possiblyother carbon-containing material and oxygen-containing gas being fed in,and with simultaneous formation of a reduction gas, the iron-containingmaterial is fused, lump coal being fed to the fusion gasifier from aboveand, together with the iron-containing material, forming a fixed bedwith a dome space above it in the fusion gasifier, thereby giving offits fraction of volatile hydrocarbons into the dome space, andpulverized-fuel burners, which are operated with a carbon carrier infine particle form and an oxygen-containing gas, passing through theshell of the fusion gasifier in a horizontal cross-sectional plan of thedome space at approximately equal distances from one another and beingdirected obliquely from above towards the surface of the fixed bed,characterized in that the operation of the pulverized-fuel burners witha carbon carrier in fine particle form and oxygen-containing gas iscontrolled in such a way that the combustion of the carbon fraction ofthe carbon carrier in fine particle form takes place in a proportion ofat least 40% to form CO₂, whereby the volatile hydrocarbons given off bythe coal are converted in an oxidizing manner.
 2. Process according toclaim 1, characterized in that the combustion of the carbon fraction ofthe carbon carrier in fine particle form takes place in a proportion ofat least 50% to form CO₂.
 3. Process according to claim 1 characterizedin that the combustion of the carbon fraction of the carbon carrier infine particle form takes place in a proportion of at least 70% to formCO₂.
 4. Process according to claim 1 characterized in that thepulverized-fuel burners are aligned in such a way that a gas-mixingturbulent flow is generated in the dome space by the burner flames. 5.Process according to claim 1 characterized in that, for generating agas-mixing turbulent flow, the pulverized-fuel burners are aligned alonglines extending askew in the same sense with respect to the verticalcentral axis of the fusion gasifier.
 6. Process according to claim 1wherein said iron-containing material in lump form is partly or fullyreduced iron sponge.